One or more embodiments of the disclosure relates to an ink jet ink for color filter and a method for preparing the same, as well as a method for preparing of a color filter.
A color filter is a major component of a liquid crystal display (LCD). White light from a backlight is filtered into red light, green light and blue light respectively through three kinds of color filters (Red, Green and Blue) of the color filter substrate, which are eventually mixed in human eyes as color images. The color filter substrate accounts for more than 30% of the costs for a liquid crystal display panel. Therefore, it is a core technique that has to be mastered in the development of the thin film transistor liquid crystal display (TFT LCD) industry. Currently, the conventional methods for the manufacture of the color filter substrate include a pigment dispersion method and an ink-jet method.
In the pigment dispersion method, color photoresists are coated on a substrate by way of spin coating, and a pixel filter layer is formed by exposure and developing. A color photoresist is a kind of photoresist with color pigment evenly dispersed in it, and has the property of light curing and thermal curing. For a color photoresist of RGB (Red:Green:Blue), three procedures, including coating, exposure and developing, are required to finally form a color filter. However, for the manufacture of large size panels, the pigment dispersion method has the disadvantages of severe waste of raw materials, as well as complicated procedures and excessively high costs of equipment.
In the ink-jet method, inks containing RGB pigments are simultaneously eject into the black matrix of a transparent substrate, and the pixel filter layer is formed with the volatilization of the solvent in the ink droplets. Using the ink-jet method, the RGB color layer can be formed in a single step, which greatly simplifies the process of manufacture and reduces the costs.
However, the performance of ink(s) has great effect on the product property when the ink jet method is employed to prepare the color filters. The current ink(s) suffers from the following primary issues: (1) a large amount of organic solvents are used as the media that give rise to a large amount of VOC (volatile organic compounds), which bring about potential risk of fire and is detrimental to the environment and the health of artisans; (2) the viscosity of the ink(s) is directly related to the molecular weight and the addition amount of resin, and is hard to adjust; and (3) the formation of the pixel filter layer requires a light curing or thermal curing step, which consumes a huge amount of energy. Therefore, the current ink jet ink(s) for color filter suffers from the common issues of high production of VOC, difficulty in adjustment of viscosity, and high energy consumption for curing the pixel filter layer.